The present invention generally relates to photovoltaic thermal hybrid solar systems and methods of operation thereof.
Definitions of certain terms discussed herein are as follows:
Photovoltaics (PV) generate electrical power by converting solar radiation into direct current electricity through semiconductors exhibiting the photovoltaic effect;
A photovoltaic cell (or PV cell, also “solar cell” or “photoelectric cell”) is a solid state device that converts energy of light directly into electricity by virtue if the photovoltaic effect;
A photovoltaic module (also “solar module”, “solar panel” or “photovoltaic panel”) is an assembly of connected photovoltaic cells;
A photovoltaic system typically includes an array of photovoltaic modules, an inverter and interconnection wiring;
A thermal collector (also “solar thermal collector”) collects heat by absorbing radiations, such as sunlight;
A heat exchanger is a device/piece of equipment to efficiently transfer heat from one medium to another;
In electronic systems, a heat sink is a component to cool a device by dissipating heat into a surrounding medium;
Solar thermal energy (STE) concerns technologies for harnessing solar energy for thermal energy (heat). STE differs from and is acknowledged to be much more efficient than photovoltaics, which converts solar energy directly into electricity;
Concentrated solar power (also “concentrating solar power” or CSP) systems use mirrors or lenses that concentrate a large area of solar thermal energy onto a small area, such that electrical power (also “power”) can be produced when concentrated light is converted to heat, which drives a heat engine (e.g., a steam turbine) connected to a power generator. Common forms of concentration are: parabolic trough, dish Stirlings, concentrating linear Fresnel reflector and solar power tower.
Concentrated photovoltaic (CPV) systems use optics (e.g., lenses) to concentrate a large amount of sunlight onto a small area of solar photovoltaic materials to generate electricity. Concentration allows for production of smaller areas of solar cells.
CPV should not to be confused with CSP: in CSP concentrated sunlight is converted to heat, and then heat is converted to electricity, whereas in CPV concentrated sunlight is converted directly to electricity using the photovoltaic effect;
Photovoltaic thermal hybrid solar collectors (also “hybrid PV/T systems” or PVT) are systems converting solar radiation into thermal and electrical energy. Such systems combine a photovoltaic cell, which converts photons into electricity, with a solar thermal collector, which captures the remaining energy and removes waste heat from the PV module. Two categories of PVT collectors are generally known:
PV/T fluid collector (air or liquid). In liquid collectors, a typical water-cooled design uses conductive-metal piping or plates attached to the back of a PV module. The working fluid is typically water or glycol. The heat from the PV cells are conducted through the metal and absorbed by the working fluid, which assumes that the working fluid is cooler than the operating temperature of the cells. In closed-loop systems this heat is either exhausted (to cool it) or transferred at a heat exchanger, where it flows to its application. In open-loop systems, this heat is used, or exhausted before the fluid returns to the PV cells;
PV/T concentrator (CPVT), wherein a concentrating system is provided to reduce the amount of solar cells needed. CPVT can reach very good solar thermal performance compared to flat PV/T collectors. However, main obstacles to CPVT are to provide good cooling of the solar cells and a durable tracking system.
A disadvantage of PV systems compared to other energy sources is the unpredictable nature of the direct solar radiation. This leads to intermittent power delivery, which has much less value than on demand power and leads to grid instabilities. Storage of electrical energy in e.g. batteries is prohibitively expensive so that the cost for a storage unit for a full day production costs much more than the solar power station. Concentrated solar power systems (CSP) that can store the collected heat can produce electricity on demand until the stored heat is dissipated. Concentrated photovoltaic (CPV) power plants have higher conversion efficiencies than PV and CSP but still suffer from intermittent power production. Concentrated photovoltaic thermal (CPVT) systems have a higher system efficiency because of the improved cooling but reject the heat to the ambient or produce low grade heat with limited utility.